A cartridge loading motion picture projector has a spindle that is movable along an arcuate path to each of several positions wherein it is adapted to be engaged with a reel within one of several sizes of cartridges that are mountable on the projector. Each of the cartridge sizes has similar locating structures, the projector spindle is received through openings in the cartridges. The openings and locating structures are positioned with respect to each other so that the openings are located along a second arcuate path if the cartridges are superimposed with their locating structures in alignment. The projector has cartridge mounting structure for positioning each of the similar locating structures on the cartridges at different positions on the projector so that the openings in the cartridges are located along the path of travel on the spindle.